If you have not filed your return yet, you can still make changes. Log back into your account and select the option to "Take me to my return" and click back into the section of the program where you need to adjust your entries. To change your refund method, return to the File section and go to Step 2, Your Refund Info.
If you have already submitted your return, you will not be able to make any changes until it is Accepted or Rejected by the IRS. If it is Accepted and you need to make changes that require filing an amended return, the IRS recommends waiting until your return is completely processed before filing an amended return. Depending on what refund method you chose, that's how the refund will be processed. If your return is rejected by the IRS, you can log back into your TurboTax account and make any changes you need and resubmit for e-filing.
To determine if you need to amend, please refer to this TurboTax FAQ:
https://ttlc.intuit.com/replies/3318732
